Nº 7 2013 > The future of time  To abolish or not to abolish the leap second?

Impact of the leap second on Japan's time-stamp system

Koichi Shibata, Time Business Forum

The integrity of time is a vital part of the modern world. It would be no exaggeration to say that it is the clock that keeps society ticking.

Computer systems such as personal computers or mobile phones support the information communication network that forms the underlying fabric of our everyday lives. All these systems operate in synch with their built-in clocks.

In recent years, increasingly sophisticated network technologies have dramatically speeded up the spread of information, and digital storage for such information has also become widespread because of its convenience.

Unlike paper documents, however, digital information can be copied and modified with great ease, making it difficult to distinguish the original document from a tampered copy.

As a countermeasure, and taking advantage of the fact that time is universal and cannot be reversed, a system that embeds a traceable time stamp in the digital document has been developed, making it possible to accurately identify the original and distinguish it from later copies. Needless to say, the time stamp must be affixed by a trusted third party.

Such a system has been standardized in Japan. Criteria were set in 2005 for Japan’s Time Business Accreditation Programme, which has subsequently been adopted by many Japanese businesses. Time stamps prove the integrity of digital documents and are used to safely share and store information throughout networks.

Japan’s accreditation programme has involved the creation of two bodies, authorized to carry out distinct services for the system and operational framework. These bodies are the Time Stamping Authority, which is responsible for distributing time stamps, and the Time Assessment Authority, which verifies the time label in the time stamps for accuracy and traceability.

With time stamps, documents such as intellectual property rights, medical records, electronic signatures, permits and inspection records can be safely stored electronically. This is highly convenient, as litigation prevention, denial measures and accountability can be achieved without the need for physical papers. As such, time stamps are becoming a valuable tool for our society.

Unfortunately, Japan’s time-stamp system has been halted three times in the past. Each of these stoppages was caused when adjustments were made to Coordinated Universal Time to include a leap second.

Under Japan’s Time Business Accreditation Programme, a time stamp must be accurate to within 1 second of its storage time. This requirement is thrown off by the leap second, forcing the system to refuse the distribution of time stamps.

The Time Stamping Authority and the Time Assessment Authority use many synchronized servers and atomic clocks to perform their time monitoring services with great accuracy. With sporadic, instantaneous events like the leap second, operators must adjust every clock. No mistake is acceptable, as this could result in issuing an inaccurately labelled time stamp.

Of the last three leap-second adjustments, two fell on New Year’s day (Japan time), and so did not cause any great problems. The third — and most recent — leap second occurred on 1 July 2012, which luckily was a Sunday in Japan, and the damage it caused was minimal. Nevertheless, each time, the operators have to suspend the service for several hours before the leap-second adjustment occurs to make sure that the whole system is synchronized when resuming the service.

In Japan, systems are adjusted for the leap second at 9 a.m., right when firms open for business. Because more and more firms have started to use the time stamping system, the damage a large-scale halt would cause on a regular workday would be catastrophic.